The present invention relates to a shift control method for an automatic transmission. More particularly, the present invention relates to a 6-speed shift control method for an automatic transmission to improve power performance and fuel economy by obtaining 6-speeds from an existing 5-speed automatic transmission.
Presently, 4-speed and 5-speed automatic transmissions are commonly used in vehicles. Such automatic transmissions are developed differently by vehicle makers depending on the type of vehicle.
However, current shift control methods have a number of drawbacks. For example, it is difficult to improve power performance and fuel economy in prior shift control methods. Furthermore, customer requirements for more speeds have not yet been satisfied.
The present invention provides a shift control method that provides six forward speeds with an existing 5-speed automatic transmission. Control of shifting is easier, power performance and fuel economy with optimal gear ratios are improved, shift quality is improved such that shift shock is minimized, and the weight of an automatic transmission is decreased.
Consequently, the present invention provides a shift control method of an automatic transmission, the automatic transmission includes a primary shift portion including two single pinion planetary gear sets, three clutches, two brakes, and a first one-way clutch. The automatic transmission also includes a secondary shift portion including a single pinion planetary gear set, a fourth clutch, a third brake, and a second one-way clutch.
In use, the automatic transmission is controlled at a first shift-speed, such that the primary shift portion has a first predetermined speed ratio and the secondary shift portion has a predetermined reduction ratio. The automatic transmission is then controlled at a second shift-speed such that the primary shift portion has a second predetermined speed ratio and the secondary shift portion has said predetermined reduction ratio. The automatic transmission is also controlled at a third shift-speed such that the primary shift portion has a speed ratio of xe2x80x9c1xe2x80x9d and the secondary shift portion has said predetermined reduction ratio. The automatic transmission is controlled at a fourth shift-speed such that the primary shift portion has a third predetermined speed ratio and the secondary shift portion has said predetermined reduction ratio. Additionally, the automatic transmission is controlled at a fifth shift-speed such that the primary shift portion has a speed ratio of xe2x80x9c1xe2x80x9d and the secondary shift portion has a speed ratio of xe2x80x9c1xe2x80x9d. Finally, the automatic transmission is controlled at a sixth shift-speed such that the primary shift portion has said third predetermined speed ratio and the secondary shift portion has a speed ratio of xe2x80x9c1xe2x80x9d.